Galápagos Lacked Any Native Amphibians. Until Hundreds of Thousands of Frogs Arrived

On her regular walk to the scientific station, scientist the researcher stoops near a small water body surrounded by thick vegetation and retrieves a small plastic audio device.

She had placed there through the night to capture the characteristic croaks of the Scinax quinquefasciatus, recognized by local scientists as an non-native threat with consequences that scientists are just beginning to understand.

Despite abounding with remarkable wildlife – including ancient large turtles, marine iguanas, and the famous finches that sparked Darwin's evolutionary theory – the Galápagos archipelago near the shoreline of Ecuador had historically been devoid of frogs and toads.

During the 1990s, this shifted. Some small tree frogs made their way from mainland the mainland to the archipelago, likely as stowaways on transport vessels.

DNA research indicate that, through time, there have been repeated accidental arrivals to the islands, and the amphibians now have a firm foothold on two locations: Isabela and Santa Cruz.

The numbers is growing so quickly that researchers have been finding it difficult to keep track, estimating numbers in the millions on each island, across developed and farming areas, but also in the conservation natural reserve.

When San José marked amphibians and attempted to recapture them in the following week and a half, she could find only a single tagged frog occasionally, indicating their populations were enormous.

They calculated six thousand frogs in a single pond. "The calculations are still very conservative," states the researcher. "I'm pretty sure there are additional numbers."

Deafening Noise and Growing Concerns

The frogs' proliferation is clear from the acoustic disruption they cause. "The number of frogs and the noise – it's truly insane," says San José.

For the scientists, their nightly mating calls are helpful in estimating their existence in far-flung areas, using audio devices like the one outside the workplace.

But local agricultural workers say the calls are so raucous they keep them up at night.

"In the rainy period, I regularly hear their calls and they're really loud," says a local coffee farmer from Santa Cruz.

"Initially it was a surprise, seeing the first frogs in the region," says the farmer, who started observing their large numbers about three years ago when one jumped on her hand as she was stepping out of her house.

Environmental Consequences Remains Unknown

The sound isn't the primary problem, however. While the species has been in the islands for nearly three decades, experts still know very little about its effect on the archipelago's precariously balanced terrestrial and aquatic environments.

On islands, it is very typical for invasive species to prosper, as they have none of their natural predators. The Galápagos counts 1,645 invasive species, many of which are significantly affecting the survival of its endemic ones.

A recent study indicates the invasive amphibians are voracious bug eaters, and might be disproportionately eating rare insects found only on the archipelago, or reducing the nutrition of the region's uncommon birds, disrupting the ecosystem balance.

Unique Characteristics and Management Difficulties

The Galápagos frogs have shown some unusual traits, including surviving in brackish water, which is uncommon for frogs.

Their development process is also extremely variable, with some larvae turning into frogs very rapidly and others taking a extended period: the researcher observed one which stayed as a larva in her laboratory for half a year.

"We really don't know this part," she says, worried the larvae could be affecting the islands' freshwater, a very limited resource in the islands.

Methods to control the amphibians in the early 2000s were largely ineffective. Conservation officers tried capturing large numbers by manual methods and gradually increasing the salinity of ponds in without success.

Studies suggests spraying caffeine – which is highly toxic to frogs – or using electrocution could help, but these approaches aren't necessarily safe for other rare island species.

Lacking solutions to more of the fundamental issues about their lifestyle and impact, culling the frogs might not even be the right way to advance, says San José.

Financial Obstacles for Study

While she hopes the increasing use of eDNA methods and genetic analysis will help her team understand of the invasive species, financial support for the research has been hard to come by.

"Everybody wants to give support for protecting frogs," says San José. "But it's harder to find funding for an invasive frog that you might want to control."